The semiconductor integrated circuit (IC) industry has experienced exponential growth. Technological advances in IC materials and design have produced generations of ICs where each generation has smaller and more complex circuits than the previous generation. In the course of IC evolution, functional density (i.e., the number of interconnected devices per chip area) has generally increased while geometry size (i.e., the smallest component (or line) that can be created using a fabrication process) has decreased. This scaling down process generally provides benefits by increasing production efficiency and lowering associated costs. Such scaling down has also increased the complexity of processing and manufacturing ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed.
As the critical dimension (CD) of a feature is scaled down, the feature may have a high aspect ratio (the ratio of the height Vs. width of the feature). Such scaling down has also increased the complexity of structure and processing of ICs and, for these advances to be realized, similar developments in IC processing and manufacturing are needed. For example, a three dimensional (3D) transistor, has been introduced to replace a planar transistor. Although existing structures and methods of fabricating semiconductor devices have been generally adequate for their intended purposes, they have not been entirely satisfactory in all respects. For example, to introduce three dimensional semiconductor structure including features with high aspect ratio raises challenges in a semiconductor device process development. Accordingly, it is desired to have improvements in this area.